1. Field of the Invention
The invention concerns a radiation shield and shielding gas conduit installed in a reactor pressure vessel between the individual components of the cooling gas circuit of the reactor. The radiation shield is removably installed within the reactor pressure vessel, more particularly in the gas conduits. The gas conduits are designed as coaxial gas conduits for the conduction of cooling gas in both directions.
2. Background of the Prior Art
It is part of the state of the art to separate by means of shielding devices the portion of the gas cooled reactor installation containing the reactor core from the portion containing components of the cooling gas circuit, such as, for example, steam generators and blowers, when both portions are housed together in the cavities of a pressure vessel. In this fashion activation of these components by direct neutron irradiation is prevented. The shielding structure must be specifically laid out so that the cooling gas will be able to flow without a substantial drop in pressure from the reactor core to the other reactor components, while preventing the passage of harmful radiation through the free cross section of the gas conduits connecting the reactor core with the reactor components.
West German Published Application No. 1 083 945 describes a reactor core shield having a cylindrical internal member and an external shielding ring, forming an S-shaped flow path of the cooling gas together with a further shielding ring. This shielding involves a high expenditure of material.
Another approach to the shielding problem that has become well known is to bend the gas conduits by 90.degree. after their passage through a shielding wall, i.e. to use angled gas conduits. This is the case for example in the THTR-300 MWe reactor and in the gas turbine power plant design of U.S. Pat. No. 4,175,001 wherein the gas heated in the reactor core is collected in a hot gas collector space and passed through a gas conduit each to the steam generators. The gas conduits for example may initially pass through a thermal shield in the horizontal direction and are then bent upward by 90.degree., so that they may be connected with the jacket of one of the steam generators.
West German Offenlegungsschrift No. 1 464 705 further describes a tubular conduit shielded against radiation immediately adjacent the reactor core. In the area of the passage through the pressure vessel of the reactor, the conduit has an expansion with a shielding block installed therein. This block has a diameter at least as large as the cross section of the conduit generally (except in the area of the block) and the flow of gas or liquid is conducted around the shielding block. This type of shielding has the disadvantage that the conduit must have a diameter that is larger in the area of the shielding block than the diameter of the conduit generally.
When the gas conduit is part of a nuclear reactor installation wherein the components of the cooling gas circuit are arranged in the recesses of a reinforced concrete pressure vessel, the components must be protected to the highest degree possible against activation by direct neutron irradiation.
In addition, the components must be readily accessible for the purposes of inspection, maintenance, repair and removal. This is particularly true for hot gas conduits connecting the hot gas collector space with components of the gas transport conduit, for example, gas turbines or heat exchangers. In order to prevent the activation of the metallic parts of these hot gas conduits, West German Offenlegungsschrift No. 25 06 293 proposes to provide shielding in the form of an annular wall in the hot gas collector space over its entire height, the wall being arranged coaxially with respect to the reactor cavity and having several rows of slits for the passage of the cooling gas.